linux-kernel - Re: iowait boost is broken

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210610152857.lqtu2xl3364l6fyh@e107158-lin.cambridge.arm.com>
Date:   Thu, 10 Jun 2021 16:28:57 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Beata Michalska <beata.michalska@....com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Valentin Schneider <valentin.schneider@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: iowait boost is broken

On 06/09/21 09:50, Quentin Perret wrote:
> On Tuesday 08 Jun 2021 at 19:46:54 (+0200), Peter Zijlstra wrote:
> > On Mon, Jun 07, 2021 at 08:10:32PM +0100, Beata Michalska wrote:
> > > So back to the expectations.
> > > The main problem, as I see it, is what do we actually want to achieve with
> > > the I/O boosting? Is it supposed to compensate the time lost while waiting
> > > for the I/O request to be completed or is is supposed to optimize the rate
> > > at which I/O requests are being made. 
> > 
> > The latter, you want to increase the race of submission.
> > 
> > > Do we want to boost I/O bound tasks by
> > > default, no limits applied  or should we care about balancing performance
> > > vs power ? And unless those expectations are clearly stated, we might not
> > > get too far with any changes, really.
> > 
> > You want to not increase power beyond what is needed to match the rate
> > of processing I suppose.
> 
> Note that in some cases we also don't care about throughput, and would
> prefer to keep the frequency for some unimportant IO bound tasks (e.g.
> background logging deamons and such). Uclamp.max indicates this to some
> extent.

In theory, one can have a user space daemon that monitors IO (via BPF?) and
auto boost via uclamp. You can have allow/disallow list per-app too to setup
the limits.

So I say rm -rf iowait_boost and let's make it a user space problem :)

/me runs

--
Qais Yousef